Cage-like filament structure for electron discharge



June 23, 1970 Yos l cm RU E AL 3,517,249

CAGE-LIKE FILAMENT STRUCTURE FOR ELECTRON DISCHARGE 2 Sheets-Sheet 1 Filed Dec.

INVENTORS K/msm uc/mma/ Yl/K/TOSH/ Yosmm TToRNEYs June 23, 1970 KIYOSHI UCHJMARU ET AL 3,517,249

CAGE-LIKE FILAMENT STRUCTURE FOR ELECTRON DISCHARGE Filed Dec. 27, 1967 2 Sheets-Sheet 2 {5M0 rasw Yes/00 4 United States Patent O Int. Cl. H013 1/94, 19/48 US. Cl. 313-278 6 Claims ABSTRACT OF THE DISCLOSURE A cage-like filament structure having a plurality of U-shaped filament strands arranged in cylindrical form with the strands secured at supported points thereon by a strand bracing structure, thereby providing a relatively simple filament structure which is subject to less deformation and which has a relatively high filament heater power efficiency.

BACKGROUND OF THE INVENTION As those knowledgeable in the art are aware, in a high power electron discharge device, the cage type filament is usually constructed by combining a plurality of filament strands in cylindrical form. One conventional filament of this type has such a construction that one end of each of a plurality of filament strands is fixed on a base a plate at a point suitably arranged on a circumference with the other end extending in cylindrical form, bundled mutually in one position, thus forming a cage shape.

When a convenient filament of such construction is to be used in a high power electron discharge device, an enlargement of the whole filament structure with an increased number of strands results in longer length of the shoulder portion of the filament, i.e., the bent portion of each strand toward the center, which emits electrons that contribute little to the operation of the electron discharge device. Thus, such a filament has the disadvantage that the proportion of the electric power to be used for the emission of the effective electrons to the total heating power applied to the filament is reduced. Thus it is seen that the heating power efficiency is reduced, because additional electric power is required that is wasted rather than used to effect electron emission.

In order to minimize the power wasted, the conventional filament has been so constructed that a center mast carrying a strand suspension plate at its top is fitted to a base plate, and the filament strands are made in U-shape, the U-shaped bent portion of each strand being suspended on the strand suspension plate. Although such a structure has been successful in reducing the wasted power because of the shortened bent portion of each period, it has the disadvantage of deformation or inclination of the filament, contact of the filament with the grid electrode, breakage of the strands, falling off of the strands from the supporting plate and other disadvantages, thus lacking reliability.

OBJECTS OF THE INVENTION An object of this invention is to provide a filament structure suitable for use in a high power electron discharge device which has the advantages of extremely 3,511,249 Patented June 23, 1970 "ice high heating power efficiency and simplicity of structure and which has also high reliability.

All of the objects, features and advantages of thi invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of the invention taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1a is a perspective view of an essential portion of a conventional filament structure,

FIGS. 1b and 1c are perspective views of further examples of conventional filament strand bracing structures,

FIG. 2 is a front view of still another example of a conventional filament,

FIG. 3 is a perspective view illustrating the essential portion of a filament structure in accordance with a first embodiment of this invention, and

FIG. 4 is a perspective view of the essential portion of a filament structure in accordance with a second embodiment of the invention.

SUMMARY OF THE INVENTION According to the present invention, a filament structure is provided wherein a plurality of generally U-shaped filament strands are arranged in cylindrical form, each of the strands being tied or secured to at least one selected supporting point on each strand by a suitable novel strand bracing structure.

The filament of this invention is capable off substantially improving the efficiency of the heating power because the portion not contributing to the electron emission is very short. Furthermore, detrimental deformation of the filament is eliminated because the expansion and contraction of the filament in the axial direction due to thermal variations is kept free, and because deformation in the radial direction is also prevented.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to FIG. 1a, a conventional filament is provided with a plurality of filament strands It) arranged in cylindrical form, the upper end of each strand being bundled together at a generally central point 11, thereby forming a cage shape. When relatively long strands are used, each strand is supported at one or more points by elements comprising a strand bracing structure 12. This strand bracing structure 12. comprises triangular-shaped binding wire 13 consisting of fine wire of a highly heat resistant metal with some flexibility, such as tungsten, molybdenum, tantalum, etc. Other strand bracing structures may also be used such as the bracing structure 12 in the shape of a disc with fins, made of a highly heatresistant metal plate, as shown in FIG. 111. FIG. 1c shows still another structure, comprising a combination of triangular binding plates 13' made of a suitable highly heatresistant metal.

When the conventional filament shown in FIG. 1 is used as the cathode element of a high power electron discharge device, the length of the shoulder portion 14 of the filament becomes longer with an increase in the diametrical dimension of the cylinder of filament strands- 10 and in the number of the strands 10. Consequently,

3 there is an increase in the electric power consumed for heating the shoulder portion 14, resulting in an increase in the power wasted.

Referring next to FIG. 2, another example of a conventional filament is shown and has such construction that a plurality of filament strands 15 of substantially U-shape are fixed on a base plate 16 with their U-shaped bent portions 17 disposed at the top, i.e., the U is in the inverted position. The bent portion 17 of each strand 15 is suspended on a strand suspension plate 19 mounted on the top of a center mast 18 which is supported in the base plate 16. In this construction, in order to maintain the strands 15 under tension, the strand suspension plate 19 is given an upward pressure in the axial direction by means of a spring 20 fitted to the center mast 18 through a metal cylinder 21 and a metal plate 22.

A filament having such a structure has a short bent portion 17 unlike the long shoulder portion 14 shown in FIG. 1 and therefore can prevent the wasting of heating power. However, with the filament of FIG. 2, difficulty is encountered in applying uniform tension to each strand, and accordingly this structure has the disadvantage that the filament may become deformed, or it may become inclined, causing it to contact the grid electrode, thereby causing the strands to break. Also, the strands 15 may fall oif the suspension plate 19 because the tension of the spring 20 is radically decreased due to the elevated temperatures. Thus it will be seen that reliability is very poor.

Referring now to FIG. 3, there is shown a first embodiment of this invention having such a construction that a plurality of filament strands 15 which are bent in substantially U-shape are arranged in cylindrical form with their bent or bridge portions 17 upward, and are fixed on a base plate (not shown). These bent portions 17 of the U-shaped elements are so arranged that the top of each bent portion is almost on the same level, each strand 15 being supported at one or more supporting points along the axis of the strand by means of a strand bracing structure 12 which is a combination of binding wires 13. One of the supporting points is preferably located adjacent to the top portion.

The filament of such construction is, because of the very short bent portion 17 of each strand 15, capable of considerably reducing the wasted heating power, i.e., improving the heating power efiiciency. Furthermore, when the filament is heated to an elevated temperature during operation, bending of the strands 15 is effectively prevented and also detrimental deformation and inclination of the filament is also prevented, because the expansion and contraction of the filament in the axial direction may freely take place, and also because radial deformation is prevented by the strand bracing structure 12.

Referring now to FIG. 4, a second embodiment of this invention is shown which is a modification of the strand bracing structure seen in the first embodiment. This embodiment has such a construction that each strand 15 is supported by a center mast 18 supported in a base plate (not shown), by a heat-resistant insulating cylinder 23 which can slide freely along the said center mast 18, and by a strand bracing structure 24 with which said insulating cylinder 23 is tied to the supporting points on each strand. This strand bracing structure 24 comprises binding wire 25 of fine, highly heat-resistant metal wire having some flexibility, tied to the strands 15 and a binding wire supporting body 26 made of a highly heat-resistant metal plate fixed to the insulating cylinder 23 to support the binding wires 25. As another example of the strand bracing structure, the binding wires 25 may be fixed to the insulating cylinder 23 directly without using the binding wire supporting body 26 in the strand bracing structure as mentioned above. As a further example, a strand bracing structure 12 as shown in FIG. 1b may be used.

Since the filament of FIG. 4 employs short, bent portions 17 as a part of the strands, as in the case of the first embodiment, the wasted heating power is extremely reduced, and further, the thermally actuated expansion and contraction in the axial direction can freely take place by reason of the insulating cylinder 23 which slides along the center mast 18. Furthermore, radial thermal expansion is restricted by means of the strand bracing structure 24, thereby eliminating almost entirely the bonding of the strands 15 and the deformation and inclination of the filament. Moreover, the filament structure shown in FIG. 4 has the advantage that the number of the strands is not limited to a multiple of 3.

In the two embodiments described above when a number of supporting points is used for each strand, either of the bracing structures of the first and the second embodiments may be employed. For instance, it is possible to use such a construction that support is made only in the neighbourhood of the top or in the neighbourhood thereof and at several intermediate points of the strands 15 by the strand bracing structure 24 and the insulating cylinder 2-3 of FIG. 4, the remaining supported points being supported by the strand bracing structure 12 of FIG. 3. Also, a construction can be employed in which the center mast 18 is shortened and in which the supported points in the upper portion of the strands are supported by the strand bracing structure 12 of FIG 3, While the supported points in the lower portion are supported by the strand bracing structure 24 and the insulating cylinder 23 of FIG. 4.

While the foregoing description sets forth the principles of the invention in connection with specific apparatus, it is to be understood that the description is made only by way of example and not as a limitation of the scope of the invention as set forth in the objects thereof and in the accompanying claims.

What is claimed is:

1. A cage-like filament structure for an electron discharge device comprising:

a plurality of substantially U-shaped filament strand elements disposed side by side to form a hollow cylinder, with the bridge portion of each U-shaped element lying around a circle at one end of the cylinder;

a base plate securing said filament strand elements at the other end of the cylinder; and

a strand bracing structure for preventing the radial deformation of the filament structure and secured to each of said strand elements at a supporting point adjacent the bridge portion thereof, said strand bracing structure being freely movable axially as the supporting points move due to thermal expansion and contraction of the strand elements.

2. The invention described in claim 1 wherein:

each U-shaped element is secured in the inverted U position. v

3. The invention described in claim 1 wherein the bridge portion of any U-shaped element comprises a small portion of the overall length of the element.

4. The invention described in claim 1 wherein said strand bracing structure comprises a network of heatresistant binding wires interconnecting similar legs of different elements.

*5. The invention described in claim 1 wherein the filament structure includes a plurality of strand bracing structures at different locations along the length of said strands.

6. The invention described in claim 1 wherein:

said strand bracing structure further includes a central mast and an apertured member freely movable in an axial direction thereon,

said mast being disposed generally parallel to said strands, and

said strand bracing structure being secured to said apertured member, whereby expansion and contraction of the filament structure upon heating and cooling is accommodated by movement of said member on said mast.

References Cited UNITED STATES PATENTS Nolte et a1. 313-278 X B01 ...1 313-279 X Wing 313-279 X Wing 313-279 X 5 JOHN HUCKERT, Primary Examiner A. J. JAMES, Assistant Examiner US. Cl. X.R. 313-276, 275, 279 

